Synthesis and Structural Characterization of a Series of New Chiral‐at‐Metal Ruthenium Allenylidene Complexes

Abstract

AbstractNew chiral‐at‐metal ruthenium indenyl PPh3 phosphoramidite allenylidene complexes have been synthesized and structurally characterized. Through thermal ligand‐exchange reactions with [RuCl(Ind)(PPh3)2], the phosphoramidite ligands (R)‐binol‐N,N‐dimethylphosphoramidite (5a), (R)‐binol‐N,N‐dibenzylphosphoramidite (5b), (R,S)‐binol‐N‐benzyl‐N‐α‐methylbenzylphosphoramidite (5c), and (R)‐catechol‐2‐methylpyrrolidinephosphoramidite [(R)‐10] were converted into the complexes [RuCl(Ind)(PPh3)(L)] [L = 5a, 79 %; 5b, 87 %; 5c, 80 %, (R)‐10, 67 %]. The complexes [RuCl(Ind)(PPh3)(5b)] and [RuCl(Ind)(PPh3)(5c)] were obtained diastereomerically pure and, by reaction with propargylic alcohols, subsequently converted into the allenylidene complexes [Ru(Ind)(PPh3)(5b)(=C=C=CRR′)]+ PF6– (R = R′ = Ph, 85 %; R = Ph, R′ = Me, 66 %; R = 2‐furyl, R′ = Me, 94 %; R = R′ = 4‐fluorophenyl, 76 %; R = 4‐methoxyphenyl, R′ = Me, 66 %) and [Ru(Ind)(PPh3)(5c)(=C=C=CRR′)]+ PF6– (R = R′ = Ph, 91 %; R = Ph, R′ = Me, 72 %; R = 2‐furyl, R′ = Me, 93 %), which were also obtained diastereomerically pure. Complex [RuCl(Ind)(PPh3)(5b)] and three of the new allenylidene complexes were characterized structurally, which showed that the chiral information was transferred from the precursor complex to the corresponding allenylidenes. Dynamic NMR experiments showed that during the synthesis of allenylidene complexes only one diastereomer was formed. The research presented herein has an impact on the chemistry of chiral allenylidene complexes as catalysts and as potential intermediates in propargylic substitution reactions.